Transmission of pictures by electricity



Dec. 27, 1927. 1,654,374 I J. w. HORTON TRANSMISSION OF PICTURES BY ELECTRICITY Filed May 17. 1924 Patented Dec. 27, 1927.

UNITED STATES PATENT OFFICE.

JOSEPH W. HORTON, OF BLOOMFIELD, NEW JERSEY, .ASSIGNOR TO WESTERN ELEC- TRIC COMPANY, INCORPORATED, 015 NEW YORK, N. Y., A CORPORATION OF NEW YORK.

Application filed May 17,

This invention relates to the transmission of images of pictures or of other objects by electricity and more particularly to means for adjusting the sending equipment.

In systems for transmittingimages of pietures or other objects by electricity it is necessary to maintain the current conditions at various points in the circuit between fairly close limits in order to preserve the proper relation between the response of the receiving equipment and the light intensities at the sending terminal. In accomplishing this result it is desirable to be able to adjust the several major circuit elements of the system independently. Such adjustment be comes the more desirable where'the Various elements are widely separated geographically,

- as is the case in any commercial system.

An object of the present invention is to accomplish the adjustment. of the sending equipment independently of the transmission circuit and of the reproducing equipment. Another object is to simplify the technique of adjustment. Still another object is to adjust the sending equipment to take into account the range of tone values in the par ticular picture which is to be transmitted.

In one embodiment of the invention 'an amplifier detector circuit provided with an indicating meter is adapted to be connected through a variable artificial line to the output circuit of the modulator of a picture sending system employing a carrier wave. The carrier wave is modulated by amplified current from a photo-electric cell. The change in carrier wave amplitude at the sendingter-minal required to produce the necessary tone value change at the reproducing terminal is predetermined interms of attenuation units, such as, miles of standard cable. The artificial line is changed by this amount coincident with a change in illumination covering the limits encountered in a particular picture and the transnlitting circuitis adjusted, so that the deflection of the indicating meter remains the'same under the two conditions. This insures a suitable response at the reproducing terminal.

The novel features which are considered characteristic of this invention are set forth with particularity in the appended claims. The invention. both as to its organization and method of operation together with other- TRANSMISSION OF PICTURES BY ELECTRICITY.

1924. Serial No. 714,180.

objects and advantages thereof, will be further explained in the following description having reference to the accompanying drawing consisting of the following figures:

Fig, 1 illustrates diagrammatically the sending equipment of a picture transmission system provided with a detector amplifier circuit according to this invention.

Fig. 2 shows the characteristics of the circuit elements of Fig. 1 under the conditions of maximum and minimum illumination of the photo-electric cell.

Fig. 3 illustrates schematically a device for causing axial movement of the picture drum simultaneously with its rotation.

Referring now to Fig. 1 a sending drum 5 carries the transparency of a picture to be transmitted. Drum 5 is adapted to be rotated and moved axially in synchronism with a reproducing drum at a reproducing terminal. A suitable synchronizing system for this purpose is disclosed in a copending a plication' of M. B. Long, Serial No. 681,34 filed December 18, 1923. An arrangement for simultaneously rotating the drum 5 and moving it axially is illustrated in Fig. 3.

The drum 5 is carried'by a shaft mounted on a carriage 56 which is slidably supported on a frame 57. A shaft 6 mounted on frame 57 is threaded over a portion of its length, which portion hasscrew engagement with a threaded collar 60 secured to carriage. The rotation of shaft 6 causes carriage 56 to slide along support 57 and at the same time causes the rotation of shaft 55 by means of gear wheels 58 and 59. Gear wheel 58 is slidable along shaft 6 but is caused to rotate therewith by means of a key sliding in a keyway. The longitudinal movement of shaft6 with respect to frame 57 is prevented by a collar 61 secured thereto. 1 Within the sending drum 5 is located a photo-electric cell 7 which is connected to the input circuit of an electron discharge device 8. Device 8 with its associated input and output circuits forms the first stage of picture current amplifier PCA. The coupling between the photo-electriccell 7 and device 8 consists of a source of potential PEB for the photo-electric cell and resistance 10. The sourceof potential PEB consists of one sec-' tion 9 and another section consisting of potentiometer 2 1, battery 25' and resistance 26.

Section 9 is variable by 4.5 bolt steps, while fine adjustments are obtained by means of potentiometer 24. A static biasing potential for device 8 is provided by battery 27. The second stage of amplifier PCA consists of electron discharge device 11 and its associated circuits; Device 11 is coupled to device 8 through a portion of battery 12 and reslstance 13. Fine adjustments of the static grld potential for device 11 are secured by means of potentiometer 28 and battery 29.

The current in photo-electric cell 7 is controlled by light from source 14 which intensely illuminates an aperture in' screen 16. An image of the aperture in screen 16 is projected upon an elemental area of the transparency of the picture mounted on drum 5 by means of lens 15. The amount of llght incident upon the photo-electric cell 7 is dependent upon the tone value of the elemental area illuminated at any given time. A picture modulator 1PM consisting of electron discharge device 22 and its associated input and output circuits has its input circuit coupled to a source of voice frequency carrier Wave CO by means of transformer 17 and resistance 18. The input circuit of the device 22 is also connected to the output circuit of amplifier PGA by means ofa resistance 20. A static grid potential for device 22 is provided by potentiometer 30 connected across battery. 31 and resistance '32. In order to facilitate the adjustment of the static output current, battery 33 of 4.5

volts is adapted to be connected in series with the input circuit of modulator PM by means of switch 34. The output circuit of tion is disclosed in a copending application of H. Elves, Serial No. 711,755, filed May 8, 1924.

The direct current flowing in. the plate circuits of devices 8, 11 and 22 is indicated by ammeters A- 1,'A-2 and A-3, respectively. I

According to this invention an amplifier detector circuit is arranged to be connected in placeof the line L by means-of switch 36 in order to facilitate the adjustment of the sending equipment. The amplifier-detector circuit may be permanently connected across line L providing its input impedance is sufliciently stable. The amplifier-detector circuit is coupled to switch 36 bymeans of transformer 42.- Electron discharge device 40 with its associated input and output circuits functions as an amplifier for the car rier wave from modulator PM, while device 41 with its associated circuits functlons as a detector. The input circuit of device 40 devices 40 and 41 are heated by current from battery 50, while plate current is supplied by battery 49. A static polarizing potential for device 40 is furnished by battery 47 and a higher polarizing potential for device 41, bybattery 48. The plate current flowing in device '41 is indicated by'ammeter A- -4.

In a commercial system the variable artificial line 43 is preferably replaced by a fixed artificial line, which may be inserted in or removed from the circuit by the operation of a key. This artificial line is so designed that it introduces an amount of attenuation corresponding to the desired change' in the amplitude of the transmitted carrier wave. This fixed artificial line is supplemented by a variable network, the adjustment of which is used to bring the detector to.approximate-. ly the most sensitive operating point.

The characteristics of the sending circuit elements will now be described by reference to Figs. 1 and 2. The potential impressedbetween the grid and filament of device 8 is represented by E1, and its value is determined by the potential of battery 27 and the potential drop across resistance '10 due to current I--O flowing therethrough. The potential impressed between the grid and filament of. device 11' is represented by 15-2, and its value is determined by that part of the battery 12 which is connected into the input circuit of device 11, the static potential of potentiometer 28, and the potential drop across resistance 13 due to current I-1 flowing presse upon the modulator PM, exclusive source CO, is represented by E-3 andits in resistance 13. The potenial 1111 value-is determined by the static "potential of potentiometer 30 and the potential drop across resistance 20 due to current I-2 flow-.

ing in resistance 20. The amplitude of the current flowing in the line L 1s represented by IL. v

Referring'now to Fig. 2, the characterlstics of the elements of Fig. 1 are shown by curves A, B, C, D, E, F and G.

Curve A shows the value, of -current I O flowing in resistance 10 corresponding to different values of light intensities incident upon the photo-electric cell 7. -Under the dark condition which is obtained when an opaque screen is inserted between the source of'light 1 4 and the photo-electric cell 7, the value of I.-O is zero. For the light bondition, which may correspond to the maximum intensity of light from the source 14 or any other intensity desired, such as that through the most transparent portion of the 105 of the potential of the carrier wave from I slope of the curve A is dependent upon the potential of battery PEB and the value of resistance 10. Between these two limiting conditions and for some distance beyond the curve A is linear.

Curve B shows the relation between the potentialE-1 impressed upon'the input circuit ofamplifier 8.and"thecurrent I-Q flowing in the" resistance 10. The point 7) corresponds to the dark condition and is dependent upon the potential of battery 27 which potential is represented by the line O7 The slope of the curve B is determined by the magnitude of resistance 10. The point on this curve corresponds to the light condition, or to the point o; on curve A.

Curve C shows the relation between the potential E1 impressed upon the input circuit of amplifier 8 and the current I1 flowing in the resistance 13. Point cl corresponds to the dark condition of curve A, or point 6 of curve B. Point e corresponds to the light condition, or the point a of curve A, or the point 0 of curve B. The shape and slope of the curve C is dependent upon the physical characteristics of device 8 and the value of resistance 13.

Curve D shows the relation between the potential E-2 impressed upon the input circuit of amplifier 11 and the current I-l flowing in the resistance 13. Point 7 corresponds to the dark condition of curve A and point 9 to the light condition. The slope of curve D is determined by the Value of resistance '13, while the intersection with the abscissa at h is dependent upon the static potential impressed upon the grid of device 11, consisting of the'potential of that portion of battery 12 which is included in the input circuit of amplifier 11 and the potential due to potentiometer 28'.

Curve E shows the relation between the potential E2 impressed upon the input circuit of amplifier 11 and the current I2 flowing in resistance 20." The shape and slope of the curve E is dependent upon the physical characteristics of the device 11 and the value of resistance 20. The points and m correspond to the dark and light conditions respectively of curve A.

Curve F shows the relation between the potential E8 impressed upon the input circuit of modulator M. exclusive of the otential dueto the carrier source. CO, and

' the current I2 flowing in the resistance 20.

The slope of curve F is dependent upon the value of resistance 20, while its intersection with the abscissa at point 29 is dependent upon the static potential determined by pot-cnt-iometer' 30 connected in the input cire cuit of the modulator PM. The points 25 and n correspond respectively to the dark and the amplitude of the carrier current point a of curve A. Between the points '1' and a, curve G is substantially linear. In order to operate only over the linear portion of curve G, it is necessary that the minimum amplitude of the carrier wave as delivered to the line under the light condition shall have a finite value greater than zero. Thus, in order that the amplitude of the carrier current delivered to the line shall also hear a linear relation to the light intensities in cident upon the photo-electric cell 7, the adjustment of the circuit elements must be such that the minimum-value of carrier current has a finite value greater than zero.

2 Method of operation.

at the photo-electric cell causes a correspond-..

ing' change in the amplitudes of the carrier wave nnpressed upon the line L or upon the" amplifier detector circuit when the J switch 36 is in the position shown.

The magnitude of this change in amplitude required for suitable reproduction at the receiving end has been determined from previous experiments. This change may .be expressed in terms of attenuation units. the attenuation unit being the attenuation causedhy one mile of standard cable at 800 cycles. In the specific arrangement of Figs. 1 and 2. the dark condition of the photoelectric cell results in the maximum amplitude of the carrier wave which is to be transmitted while the lightcondition results in the minimum amplitude.

In order to adjust the equipment for transmitting a given pi-cture,an opaque screen is first placed in the path of the light falling upon the photoelectric cell so that no light is incident upon the cell. The elements of the picture amplifier PCA and of the picture modulator PM are now adjusted so that the amplitude of the carrier delivered to the line has about the maximum value which can he obtained without departing from a linear relation between the amplitude of this carrier and the potential In other words the adjustment is made so that for no illumination of the photoelectric cell the line current corresponds to the point 8 on curve G of Fig; 2.

In making this adjustment, attention may he called-to the fact that the characteristics (X E. and G of Fig. 2 are dependent upon the physical properties of the devices 8, 11 and 22 respectively. The characteristics B,

I values of resistances 10, 13, and respecammeter tively and upon the potentials associated therewith, as hereinbefore described. These characteristics may, therefore, be adjusted by a suitable choice of the values of the re sistances and potentials already referred to. This adjustment is so made that the operating limits of the system fall upon linear portions of the characteristics C, E, and G. In making this adjustment, care mustbe ob served to keep the values of the several resistances of the static potentials within limits which insure the stable performance of the circuit. For example the sensitivity of the amplifier PCA may be increased by an increase in the value of the resistance 10, this increase reacting to cause an increase in the potential E1 for a given change in illumination. A large value for resistance 10 is, however, not desired since it makes the sys tem unstable and susceptible to interference from external disturbances. 'The amplification of the detector amplifier is then adjusted so that the variation in the current through the ammeter A4 for a given variation in the amphtude of the lmpressed carrier wave is near its maximum value. The deflection of the ammeter -A4 is noted, The light incident upon the photoelectric. cell is next adjusted to have a value corresponding to,

the transmission through the most transparent part of the picture transparency. The attenuation of the artificial line 43 is decreased by an amount corresponding to the decrease in current which this change in illumination is desired to produce, the amount of this current change being such as is known to reduce the response at the receiving end to the P1126! value. The deflection of the 4 is now brought to the previously noted value by an adjustment of the source of potential FEB or the-resistance 10. It will be apparent from an examination of Fig. 2 that the curves A, and B are the only characteristics which can be, al ter ed without aifecting the amplitude of the carrier current corresponding to the dark condition. A readjustmentof one or both of these characteristics, therefore, affords the most convenient means, so that a given change in illumination produces a desired change in current. 'The slope of the characteristic A is dependent upon the potential of the source of potential PEB and upon the resistance 10. The slope of the curve Bis dependent upon the resistance 10; The pr fe'rred adjustment is that aifecting the source an adjustment which restores the deflection of the ammeter A-4 to the originally noted value, it is assured that the reduction in the amplitude of the line current resulting from the. given illumination of the photoelectric cell corresponds exactly" to the reduction in the attenuation of the artificial line 43.

The same procedure is followed for each picture to be transmitted. The same or any desired range of variation in the amplitude of the carrierwave is thus insured foreach picture so that suitable reproduction will result. A great advantage in this method of adjustment lies in the fact that the testing equipment and the picture to be transmitted are both at the same location. The result of the test can be observed by the same op-- erator. The invention therefore permits of simplification in the technique of transmitting pictures between geographically separated points. I

While the invention has been described in I termining and limiting the transmitted current to a range within the range of the reproducing apparatus.

2.- In a system for the electrical transmission ofimages of pictures or of other ob ects, sending apparatus for producing current variations in accordance with .elemental tone values of a picture or other object whose image is to be transmitted, reproducing equipment having a predetermined adjustment, means for adjusting the sending apparatus to produce an operating current lying between any two desired limits regardless of the tone values of the picture or other object whose image is to be transmitted, and means at the sending terminal for determining these adjustments independently of the reproducing equipment.

3. In a system for transmitting images of pictures or of-other objects by electricity, a

modulator, a source of carrier wave. a photoimpress current from the carrier wave source and from said amplifier upon the input circuit of said modulator, a test circuit connected to the output circuit of said modulator comprising an artificial line and an indicating device, said device giving one indication for the dark condition of thephotoelectric cell, means to change the value of the artificial line, and means to vary the potential impressed upon the photo-electric two desired liniits regardless of the tone value of the picture or other object whose image is to be transmitted, and corresponding to the tone value change for which the reproducing apparatus is adjusted, and means at the sending terminal for determin ing the adjustments of the sending apparatus independently of the reproducing apparatus.

5. In a system for transmitting images of pictures or of other objects, an electron discharge modulator having an input and an output circuit, the value of the output carrier wave depending upon the input potential exclusive of the carrier wave potential, a test circuit connected to the output circuit of the modulator, an indicating device and a variable attenuation device for said test circuit, means to adjust the input potential of said modulator, exclusive of said carrier wave potential, to give an indication on said'indicating device with a given setting of said attenuation device, means to change the setting of the attenuation device by an amount by which it is desired to change the output current of the modulator, and other means to change the input potential of said modulator exclusive of said carrier wave potential, so that. the indicating device gives the same indication as before, whereby the change in the input potential required to effect a desired change in the output current is readily determined.

6. In a system for transmitting images of pictures or of other objects, an electron dis charge modulator having an input and an output circuit, the characteristic between input potential exclusive of the carrier wave potential, and output of modulated carrier wave being substantially linear over a range of output current neither limit of which is zero, a test circuit connected to the output circuit of said modulator, an indicating device and a variable attenuation device for said test circuit, means to adjust the input potential of said modulator, exclusive of the carrier wave potential, within said linear range'to give an indication on said indicating device with a given setting of said attenuation device, means to change the setting of the attenuation device by an amount by which it is desired to change the output current of said modulator, and means. to

change the input potential of said modulator, exclusive of said carrier wave, so that the indicating device gives the same indication as before, whereby thechange in input po tential required to eli'ect a desired change in output current is readily determined.

7. In a system for transmitting images of pictures or of other objects electrically, an electron discharge modulator havingv an input and an output circuit, the characteristic between input potential, exclusive of the carrier wave potential, and output of modulated. carrier wave being substantially linear over a considerable range, a test circuit connected to the output circuit of said modulator, an indicating device and a variable attenuation device for said test circuit, a photoelectric cell associated with the input circuit of said modulator for impressing input potentials, exclusive of said carrier wave potential, upon said modulator to control the output of carrier wave therefrom, means to adjust said input potential under one condition of light intensity with said cell to give an indication on said indicating device with a given setting of said attenuation device, means to change the setting of the attenuation device by an amount by which it is desired to change the output current of the modulator, additional means to adjust said input potential under another condition of light intensity within said cell, so that the indicating device will give the same indication as before, whereby changes of light intensity within said cell from maximum to minimum will cause the desired change in the output of carrier wave.

8. in a system for transmitting images of pictures'or of other objects electrically, an electron discharge modulator having an input and an out-put circuit, the characteristic between input potential, exclusive of the carrier wave potential, and output of modulated carrier wave being substantially linear over a range of output current neither limit of which is zero, a test circuit connected to the output clrcult of said modulator, an indic ating device and a variable attenuation device for said test circuit, a photo-electric cell energized by light intensities corresponding to the tone values of elemental areas of the picture'to be transmitted, a two-' stage resistance-coupled electron discharge amplifier for impressing potentials, exclusive of the carrier wave potential, upon the input circuit of said modulator, the values of which are dependent opon the lignt intenity within the photo-electric cell, means to adjust said amplifier and modulator under the condition of light intensity within said cell corresponding to the most dense elemental area of said picture so that the output carrier wave corresponds to one point on the linear portion of said characteristic curve, which gives one indication on said ting of the attenuation device by an amount' indicating device with a given setting of said attenuation device, means to change the setcorresponding to a desired change in the output current of the modulator, and additional means to adjust said amplifierunder the condition oflight' intensity within saidcell corresponding .to the most transparent element area of said picture so that the output carrier .wave corresponds to another point on the linear portion of said characteristic curve and causes the indicating device to ive the same indications as before, Wherey the output carrier Wave will vary linearly from one extreme to the other as the light intensity within the photo-electric cell varies between limits corresponding to the most dense and most transparent portions ofthe picture.

- 9, In' 'a'system for transmitting images of pictures or of other objects electrically,i'

means to modulate a carrier wave in accordance with the tone values of elemental areas of the picture or other object to be transmitted, means to adjust said-modulating 'means so that the output of modulated carrier wave varies between predetermined limits, the variation depending upon the maximum and minimum tone values of the elemental areas of the picture or other object, and means independent of the reproducing means for indicating the correctness :of the adjustment.

10. In a system for transmitting images of pictures. or of other ob ects electrically, means to modulate a carrier wave in accordance' with the tone values of elemental areas modulating means so that the output of modulated carrier wave varies between pre-. determined limits, which limits dependupon the maximum and minimum tone values or the elemental areas of the picture or other object, and testing means at'the sending terminal to indicate the correctness of the adjustment.

11.;In a system for of pictures or of other objects electrically, meansto modulate'a carrier wave in accordance with the tone values of elemental areas transmitting images i I of pictures or of other objects electrically,

means to modulate a carrier wave in accordance with the tone val es of elemental areas of thepicture to be tr'nsmitted, means to adjust said modulating means so that the output of modulated carrier wave varies between predetermined limits, which limits de pend upon the maximum and minimum tone Values of the picture or other object, and a test circuit consisting of an artificial line,

an electron discharge amplifier and detector and a current indicatin the correctness of the ad ustment.

In witness whereof, I hereunto subscribe meter to indicate i my name this 17th day of-May A. D., 1924;.

JosEPH w. HORlON. 

